Synthesis of Triamidoamine Ligands of the Type (ArylNHCH2CH2)3N and Molybdenum and Tungsten Complexes That Contain an [(ArylNCH2CH2)3N]3-Ligand

Abstract

Aryl bromides react with (H₂NCH₂CH₂)₃N in a reaction catalyzed by Pd₂(dba)₃ in the presence of BINAP and NaO-t-Bu to give the arylated derivatives (ArylNHCH₂CH₂)₃N [Aryl = C₆H₅ (1a), 4-FC₆H₄ (1b), 4-t-BuC₆H₄ (1c ), 3,5-Me₂C₆H₃ (1d), 3,5-Ph₂C₆H₃ (1e), 3,5-(4-t-BuC₆H₄)₂C₆H₃ (1f), 2-MeC₆H₄ (1g), 2,4,6-Me₃C₆H₂ (1h)]. Reactions between (ArNHCH₂CH₂)₃N (Ar = C₆H₅, 4-FC₆H₄, 3,5-Me₂C₆H₃, and 3,5-Ph₂C₆H₃) and Mo(NMe₂)₄ in toluene at 70 °C lead to [(ArNHCH₂CH₂)₃N]Mo(NMe₂) complexes in yields ranging from 64 to 96%. Dimethylamido species (Ar = 4-FC₆H₄, 3,5-Me₂C₆H₃) could be converted into paramagnetic [(ArNHCH₂CH₂)₃N]MoCl species by treating them with 2,6-lutidinium chloride in tetrahydrofuran (THF). The “direct reaction” between 1a − f and MoCl₄(THF)₂ in THF followed by 3 equiv of MeMgCl yielded [(ArNHCH₂CH₂)₃N]MoCl species (3a − f) in high yield. If 4 equiv of LiMe instead of MeMgCl are employed in the direct reaction, then [(ArNHCH₂CH₂)₃N]MoMe species are formed. Tungsten species, [(ArNHCH₂CH₂)₃N]WCl, could be prepared by analogous “direct” methods. Cyclic voltammetric studies reveal that MoCl complexes become more difficult to reduce as the electron donating ability of the [(ArNHCH₂CH₂)₃N]^3- ligand increases, and the reductions become less reversible, consistent with ready loss of chloride from {[(ArNHCH₂CH₂)₃N]MoCl}^-. Tungsten complexes are more difficult to reduce, and reductions are irreversible on the CV time scale.